Exhibit 99.B(d)(78)

INVESTMENT SUB-ADVISORY AGREEMENT

SEI INSTITUTIONAL MANAGED TRUST

AGREEMENT made as of this 29th day of September, 2005 between SEI Investments Management Corporation (the “Adviser”) and Smith Breeden Associates, Inc. (the “Sub-Adviser”).

WHEREAS, SEI Institutional Managed Trust, a Massachusetts business trust (the “Trust”), is registered as an open-end management investment company under the Investment Company Act of 1940, as amended (the “1940 Act”); and

WHEREAS, the Adviser has entered into an Investment Advisory Agreement dated January 28, 1997 (the “Advisory Agreement”) with the Trust, pursuant to which the Adviser acts as investment adviser to the series of the Trust set forth on Schedule A attached hereto (each, a “Fund”), as such Schedule may be amended by mutual agreement of the parties hereto; and

WHEREAS, the Adviser, with the approval of the Trust, desires to retain the Sub-Adviser to provide investment advisory services to the Adviser in connection with the management of the Fund, and the Sub-Adviser is willing to render such investment advisory services.

NOW, THEREFORE, the parties hereto agree as follows:

1. Duties of the Sub-Adviser. Subject to supervision by the Adviser and the Trust’s Board of Trustees, the Sub-Adviser shall manage all of the securities and other assets of the Fund entrusted to it hereunder (the “Assets”), including the purchase, retention and disposition of the Assets, in accordance with the Fund’s investment objectives, policies and restrictions as stated in the Fund’s prospectus and statement of additional information, as currently in effect and as amended or supplemented from time to time and delivered to the Sub-Adviser (referred to collectively as the “Prospectus”), and subject to the following:

(a) The Sub-Adviser shall, subject to any direction of the Adviser and Paragraph 1(b), determine from time to time what Assets will be purchased, retained or sold by the Fund, and what portion of the Assets will be invested or held uninvested in cash.

(b) In the performance of its duties and obligations under this Agreement, the Sub-Adviser shall act in conformity with the Trust’s Declaration of Trust (as defined herein) and the Prospectus and with any instructions and directions of the Adviser and of the Board of Trustees of the Trust and will conform to and comply with the requirements of the 1940 Act, the Internal Revenue Code of 1986 (the “Code”), and all other applicable federal and state laws and regulations, as each is amended from time to time (collectively, “Relevant Guidance and Laws”). The Adviser may place the management of the investment portfolio of the Fund with one or more sub-advisers, including the Sub-Adviser. The Sub-Adviser shall only be responsible for the Assets’ compliance with the Relevant Guidance and Laws and shall have no liability for any violation by the Fund of Relevant Guidance and Laws that is caused by the actions of another sub-adviser.

(c) The Sub-Adviser shall determine the Assets to be purchased or sold by the Fund as provided in subparagraph (a) and will place orders with or through such persons, brokers or dealers to carry out the policy with respect to brokerage set forth in the Fund’s Prospectus or as the Board of Trustees or the Adviser may direct from time to time, in conformity with all federal securities laws. In executing Fund transactions and selecting brokers or dealers, the Sub-Adviser will use its best efforts to seek on behalf of the Fund best execution. In assessing best execution for any transaction, the Sub-Adviser shall consider all factors that it deems relevant, including the breadth of the market in the security, the price of the security, the financial condition and execution capability of the broker or dealer, and the reasonableness of the commission, if any, both for the specific transaction and on a continuing basis. In evaluating best execution, and in selecting the broker-dealer to execute a particular transaction, the Sub-Adviser may also consider the brokerage and research services provided (as those terms are defined in Section 28(e) of the Securities Exchange Act of 1934 (the “Exchange Act”)). Consistent with any guidelines established by the Board of Trustees of the Trust and Section 28(e) of the Exchange Act, the Sub-Adviser is authorized to pay to a broker or dealer who provides such brokerage and research services a commission for executing a portfolio transaction for the Fund which is in excess of the amount of commission another broker or dealer would have charged for effecting that transaction if, but only if, the Sub-Adviser determines in good faith that such commission was reasonable in relation to the value of the brokerage and research services provided by such broker or dealer — viewed in terms of that particular transaction or in terms of the overall responsibilities of the Sub-Adviser to its discretionary clients, including the Fund. In addition, the Sub-Adviser is authorized to allocate purchase and sale orders for securities to brokers or dealers (including brokers and dealers that are affiliated with the Adviser, Sub-Adviser or the Trust’s principal underwriter) if the Sub-Adviser believes that the quality of the transaction and the commission are comparable to what they would be with other qualified firms. In no instance, however, will the Fund’s Assets be purchased from or sold to the Adviser, Sub-Adviser, the Trust’s principal underwriter, or any affiliated person of either the Trust, Adviser, the Sub-Adviser or the principal underwriter, acting as principal in the transaction, except to the extent permitted by the Securities and Exchange Commission (“SEC”) and the 1940 Act.

(d) The Sub-Adviser shall maintain all books and records with respect to transactions involving the Assets required by subparagraphs (b)(5), (6), (7), (9), (10) and (11) and paragraph (f) of Rule 31a-1 under the 1940 Act. The Sub-Adviser shall provide to the Adviser or the Board of Trustees such periodic and special reports, balance sheets or financial information, and such other information with regard to its affairs as the Adviser or Board of Trustees may reasonably request.

The Sub-Adviser shall keep the books and records relating to the Assets required to be maintained by the Sub-Adviser under this Agreement and shall timely furnish to the Adviser all information relating to the Sub-Adviser’s services under this Agreement needed by the Adviser to keep the other books and records of the Fund required by Rule 31a-1 under the 1940 Act. The Sub-Adviser shall also furnish to the Adviser any other

information relating to the Assets that is required to be filed by the Adviser or the Trust with the SEC or sent to shareholders under the 1940 Act (including the rules adopted thereunder) or any exemptive or other relief that the Adviser or the Trust obtains from the SEC. The Sub-Adviser agrees that all records that it maintains on behalf of the Fund are property of the Fund and the Sub-Adviser will surrender promptly to the Fund any of such records upon the Fund’s request; provided, however, that the Sub-Adviser may retain a copy of such records. In addition, for the duration of this Agreement, the Sub-Adviser shall preserve for the periods prescribed by Rule 31a-2 under the 1940 Act any such records as are required to be maintained by it pursuant to this Agreement, and shall transfer said records to any successor sub-adviser upon the termination of this Agreement (or, if there is no successor sub-adviser, to the Adviser).

(e) The Sub-Adviser shall provide the Fund’s custodian on each business day with information relating to all transactions concerning the Fund’s Assets and shall provide the Adviser with such information upon request of the Adviser.

(f) The investment management services provided by the Sub-Adviser under this Agreement are not to be deemed exclusive and the Sub-Adviser shall be free to render similar services to others, as long as such services do not impair the services rendered to the Adviser or the Trust.

(g) The Sub-Adviser shall promptly notify the Adviser of any financial condition that is likely to impair the Sub-Adviser’s ability to fulfill its commitment under this Agreement.

(h) (i) Except under the circumstances set forth in subsection (ii), the Sub-Adviser shall not be responsible for reviewing proxy solicitation materials or voting and handling proxies in relation to the securities held as Assets in the Fund. If the Sub-Adviser receives a misdirected proxy, it shall promptly forward such misdirected proxy to the Adviser.

(ii) The Sub-Adviser hereby agrees that upon 60 days’ written notice from the Adviser, the Sub-Adviser shall assume responsibility for reviewing proxy solicitation materials and voting proxies in relation to the securities held as Assets in the Fund in accordance with the Sub-Adviser’s proxy voting policy. As of the time the Sub-Adviser shall assume such responsibilities with respect to proxies under this sub-section (ii), the Adviser shall instruct the custodian and other parties providing services to the Fund to promptly forward misdirected proxies to the Sub-Adviser.

(i) In performance of its duties and obligations under this Agreement, the Sub-Adviser shall not consult with any other sub-adviser to the Fund or a sub-adviser to a portfolio that is under common control with the Fund concerning the Assets, except as permitted by the policies and procedures of the Fund. The Sub-Adviser shall not provide investment advice to any assets of the Fund other than the Assets.

(j) On occasions when the Sub-Adviser deems the purchase or sale of a security to be in the best interest of the Fund as well as other clients of the Sub-Adviser, the Sub-Adviser may, to the extent permitted by applicable law and regulations, aggregate the order for securities to be sold or purchased. In such event, the Sub-Adviser will allocate securities so purchased or sold, as well as the expenses incurred in the transaction, in a manner the Sub-Adviser reasonably considers to be equitable and consistent with its fiduciary obligations to the Fund and to such other clients under the circumstances.

(k) In accordance with Relevant Guidance and Laws, the Sub-Adviser shall have full power and authority, in addition to other authorizations and powers given to the Sub-Adviser in this Agreement, on behalf of the Fund to:

(i) pledge any security or other asset of the Fund or establish safekeeping, brokerage or futures accounts in the name of the Fund for the purpose of providing collateral to brokers, issuers or dealers with respect to transactions for the Fund and to permit rehypothecation of any security or other asset of the Fund; and

(ii) in the name of the Fund, and which shall be binding on the Fund, negotiate and enter into agreements and contracts (including, but not limited to, brokerage agreements, International Swap Dealers Association (ISDA) master agreements and schedules thereto, other master agreements, investment transactions, confirmations of investment transactions and related documents for investment transactions), and make representations (including representations regarding the purchase of securities or other assets for investment) that the Sub-Adviser deems appropriate to carry out its duties and services hereunder.

(l) The Sub-Adviser does not guarantee: (i) against Fund losses; (ii) the future performance of the Fund or any specific level of performance; (iii) the success of any investment strategy that the Sub-Adviser may use; or (iv) the success of the Sub-Adviser’s overall performance.

Services to be furnished by the Sub-Adviser under this Agreement may be furnished through the medium of any of the Sub-Adviser’s partners, officers, employees or control affiliates; provided, however, that the use of such mediums does not relieve the Sub-Adviser from any obligation or duty under this Agreement.

2. Duties of the Adviser. The Adviser shall continue to have responsibility for all services to be provided to the Fund pursuant to the Advisory Agreement and shall oversee and review the Sub-Adviser’s performance of its duties under this Agreement; provided, however, that in connection with its management of the Assets, nothing herein shall be construed to relieve the Sub-Adviser of responsibility for compliance with the Trust’s Declaration of Trust (as defined herein), the Prospectus, the written instructions and directions of the Board of Trustees of the Trust (provided that each such document has been delivered to the Sub-Adviser), the requirements of the 1940 Act, the Code, and all other applicable federal and state laws and regulations, as each is amended from time to time.

3. Delivery of Documents.

(a) The Adviser has furnished the Sub-Adviser with copies of each of the following documents, and, to the extent such document affects the Sub-Adviser’s duties and obligations under this Agreement, will furnish any and all future amendments to such documents to the Sub-Adviser:

(i) The Trust’s Agreement and Declaration of Trust, as filed with the Secretary of State of the Commonwealth of Massachusetts (such Agreement and Declaration of Trust, as in effect on the date of this Agreement and as amended from time to time, herein called the “Declaration of Trust”);

(ii) By-Laws of the Trust (such By-Laws, as in effect on the date of this Agreement and as amended from time to time, are herein called the “By-Laws”); and

(iii) Prospectus of the Fund.

(b) The Sub-Adviser has furnished to the Adviser a copy of the Sub-Adviser’s Form ADV Part II at least 48 hours prior to the execution of this Agreement.

4. Compensation to the Sub-Adviser. For the services to be provided by the Sub-Adviser pursuant to this Agreement, the Adviser will pay the Sub-Adviser, and the Sub-Adviser agrees to accept as full compensation therefor, a sub-advisory fee at the rate specified in Schedule B which is attached hereto and made part of this Agreement. The fee will be calculated based on the average daily value of the Assets under the Sub-Adviser’s management and will be paid to the Sub-Adviser monthly. If this Agreement is terminated at any time other than the end of the month, the Sub-Adviser shall receive a fee that is pro-rated based on the number of days in the month that this Agreement was in effect. For the avoidance of doubt, notwithstanding the fact that the Agreement has not been terminated, no fee will be accrued under this Paragraph 4 with respect to any day that the value of the Assets under the Sub-Adviser’s management equals zero. Except as may otherwise be prohibited by law or regulation (including any then current SEC staff interpretation), the Sub-Adviser may, in its discretion and from time to time, waive a portion of its fee.

5. Limitation of Liability of Sub-Adviser; Indemnification. The Sub-Adviser shall not be liable for any error of judgment or for any loss suffered by the Fund or Adviser in connection with the performance of its obligations under this Agreement, except a loss resulting from a breach of fiduciary duty with respect to the receipt of compensation for services (in which case any award of damages shall be limited to the period and the amount set forth in Section 36(b)(3) of the 1940 Act), or a loss resulting from willful misfeasance, bad faith or gross negligence on the Sub-Adviser’s part in the performance of its duties or from reckless disregard of its obligations and duties under this Agreement, except as may otherwise be provided under provisions of applicable law which cannot be waived or modified hereby.

The Sub-Adviser shall indemnify and hold harmless the Fund and the Adviser from and against any and all claims, losses, liabilities or damages (including reasonable attorney’s fees and other related expenses) resulting from the Sub-Adviser’s breach of fiduciary duty with respect to the receipt of compensation for services, or from willful misfeasance, bad faith or gross negligence on the part of the Sub-Adviser in connection with the performance of the Sub-Adviser’s obligations under this Agreement, or from the Sub-Adviser’s reckless disregard of its obligations and duties under this Agreement; provided, however, that the Sub-Adviser’s obligation under this Paragraph 5 with respect to indemnifying the Adviser shall be reduced to the extent that the claim against, or the loss, liability or damage experienced by the Adviser, is caused by or is otherwise directly related to the Adviser’s own willful misfeasance, bad faith or gross negligence, or to the reckless disregard of its duties under this Agreement.

The Adviser shall indemnify and hold harmless the Sub-Adviser from and against any and all claims, losses, liabilities or damages (including reasonable attorney’s fees and other related expenses) resulting from the Adviser’s willful misfeasance, bad faith or gross negligence in connection with the performance of the Adviser’s obligations under this Agreement, or from the Adviser’s reckless disregard of its obligations and duties under this Agreement; provided, however, that the Adviser’s obligation under this Paragraph 5 with respect to indemnifying the Sub-Adviser shall be reduced to the extent that the claim against, or the loss, liability or damage experienced by the Sub-Adviser, is caused by or is otherwise directly related to the Sub-Adviser’s own willful misfeasance, bad faith or gross negligence, or to the reckless disregard of its duties under this Agreement.

As used in this Paragraph 5, the term “Sub-Adviser,” “Adviser” and “Fund” shall include each entity’s respective officers, directors/trustees, employees and other corporate agents, as well as the entity itself.

6. Duration and Termination. This Agreement shall become effective upon approval by the Trust’s Board of Trustees and its execution by the parties hereto. Pursuant to the exemptive relief obtained in the SEC Order dated April 29, 1996, Investment Company Act Release No. 21921, approval of the Agreement by a majority of the outstanding voting securities of the Fund is not required.

This Agreement shall continue in effect for a period of more than two years from the date hereof only so long as continuance is specifically approved at least annually in conformance with the 1940 Act; provided, however, that this Agreement may be terminated with respect to the Fund (a) by the Fund at any time, without the payment of any penalty, by the vote of a majority of Trustees of the Trust or by the vote of a majority of the outstanding voting securities of the Fund, (b) by the Adviser at any time, without the payment of any penalty, on not more than 60 days’ nor less than 30 days’ written notice to the Sub-Adviser, or (c) by the Sub-Adviser at any time, without the payment of any penalty, on 90 days’ written notice to the Adviser. This Agreement shall terminate automatically and immediately in the event of its assignment, or in the event of a termination of the Advisory Agreement with the Trust. As used in this Paragraph 6, the

terms “assignment” and “vote of a majority of the outstanding voting securities” shall have the respective meanings set forth in the 1940 Act and the rules and regulations thereunder, subject to such exceptions as may be granted by the SEC under the 1940 Act.

7. Compliance Program of the Sub-Adviser. The Sub-Adviser hereby represents and warrants that:

(a) in accordance with Rule 206(4)-7 under the Investment Advisers Act of 1940, as amended (the “Advisers Act”), the Sub-Adviser has adopted and implemented and will maintain written policies and procedures reasonably designed to prevent violation by the Sub-Adviser and its supervised persons (as such term is defined in the Advisers Act) of the Advisers Act and the rules the SEC has adopted under the Advisers Act; and

(b) to the extent that the Sub-Adviser’s activities or services could affect a Fund, the Sub-Adviser has adopted and implemented and will maintain written policies and procedures that are reasonably designed to prevent violation of the “federal securities laws” (as such term is defined in Rule 38a-1 under the 1940 Act) by the Fund and the Sub-Adviser (the policies and procedures referred to in this Paragraph 7(b), along with the policies and procedures referred to in Paragraph 7(a), are referred to herein as the Sub-Adviser’s “Compliance Program”).

8. Reporting of Compliance Matters.

(a) The Sub-Adviser shall promptly provide to the Trust’s Chief Compliance Officer (“CCO”) the following documents:

(i) copies of all SEC examination correspondences, including correspondences regarding books and records examinations and “sweep” examinations, in which the SEC identified any concerns, issues or matters (such correspondences are commonly referred to as “deficiency letters”) relating to any aspect of the Sub-Adviser’s investment advisory business and the Sub-Adviser’s responses thereto;

(ii) a report of any material violations of the Sub-Adviser’s Compliance Program or any “material compliance matters” (as such term is defined in Rule 38a-1 under the 1940 Act) that have occurred with respect to the Sub-Adviser’s Compliance Program;

(iii) a report of any material changes to the policies and procedures that compose the Sub-Adviser’s Compliance Program;

(iv) a copy of the Sub-Adviser’s chief compliance officer’s report (or similar document(s) which serve the same purpose) regarding his or her annual review of the Sub-Adviser’s Compliance Program, as required by Rule 206(4)-7 under the Advisers Act; and

(v) an annual (or more frequently as the Trust’s CCO may reasonably request) representation regarding the Sub-Adviser’s compliance with Paragraphs 7 and 8 of this Agreement.

(b) The Sub-Adviser shall also provide the Trust’s CCO with:

(i) reasonable access to the testing, analyses, reports and other documentation, or summaries thereof, that the Sub-Adviser’s chief compliance officer relies upon to monitor the effectiveness of the implementation of the Sub-Adviser’s Compliance Program; and

(ii) reasonable access, during normal business hours, to the Sub-Adviser’s facilities for the purpose of conducting pre-arranged on-site compliance related due diligence meetings with personnel of the Sub-Adviser

9. Governing Law. This Agreement shall be governed by the internal laws of the Commonwealth of Massachusetts, without regard to conflict of law principles; provided, however, that nothing herein shall be construed as being inconsistent with the 1940 Act.

10. Severability. Should any part of this Agreement be held invalid by a court decision, statute, rule or otherwise, the remainder of this Agreement shall not be affected thereby. This Agreement shall be binding upon and shall inure to the benefit of the parties hereto and their respective successors.

11. Notice. Any notice, advice or report to be given pursuant to this Agreement shall be deemed sufficient if delivered or mailed by registered, certified or overnight mail, postage prepaid addressed by the party giving notice to the other party at the last address furnished by the other party:

To the Adviser at:	SEI Investments Management Corporation One Freedom Valley Road Oaks, PA 19456 Attention: Legal Department
To the Trust’s CCO at:	SEI Investments Management Corporation One Freedom Valley Road Oaks, PA 19456 Attention: Thomas D. Jones
To the Sub-Adviser at:	Smith Breeden Associates, Inc. 100 Europa Drive, Suite 200 Chapel Hill, NC 27517 Attention: Mary Mewkill

12. Non-Hire/Non-Solicitation. The Sub-Adviser hereby agrees that so long as the Sub-Adviser provides services to the Adviser or the Trust and for a period of one year following the date on which the Sub-Adviser ceases to provide services to the Adviser and the Trust, the Sub-Adviser shall not for any reason, directly or indirectly, on the Sub-Adviser’s own behalf or on behalf of others, hire any person employed by the Adviser, whether or not such person is a full-time employee or whether or not any person’s employment is pursuant to a written agreement or is at-will. The Sub-Adviser further agrees that, to the extent that the Sub-Adviser breaches the covenant described in this paragraph, the Adviser shall be entitled to pursue all appropriate remedies in law or equity.

13. Entire Agreement. This Agreement embodies the entire agreement and understanding between the parties hereto, and supersedes all prior agreements and understandings relating to this Agreement’s subject matter. This Agreement may be executed in any number of counterparts, each of which shall be deemed to be an original, but such counterparts shall, together, constitute only one instrument.

In the event the terms of this Agreement are applicable to more than one portfolio of the Trust (for purposes of this Paragraph 13, each a “Fund”), the Adviser is entering into this Agreement with the Sub-Adviser on behalf of the respective Funds severally and not jointly, with the express intention that the provisions contained in each numbered paragraph hereof shall be understood as applying separately with respect to each Fund as if contained in separate agreements between the Adviser and Sub-Adviser for each such Fund. In the event that this Agreement is made applicable to any additional Funds by way of a Schedule executed subsequent to the date first indicated above, provisions of such Schedule shall be deemed to be incorporated into this Agreement as it relates to such Fund so that, for example, the execution date for purposes of Paragraph 6 of this Agreement with respect to such Fund shall be the execution date of the relevant Schedule.

14. Miscellaneous.

(a) A copy of the Declaration of Trust is on file with the Secretary of State of the Commonwealth of Massachusetts, and notice is hereby given that the obligations of this instrument are not binding upon any of the Trustees, officers or shareholders of the Fund or the Trust.

(b) Where the effect of a requirement of the 1940 Act reflected in any provision of this Agreement is altered by a rule, regulation or order of the SEC, whether of special or general application, such provision shall be deemed to incorporate the effect of such rule, regulation or order.

IN WITNESS WHEREOF, the parties hereto have caused this Agreement to be executed by their officers designated below as of the day and year first written above.

SEI Investments Management Corporation		Smith Breeden Associates, Inc.


By:		By:

/s/ Sofia A. Rosala		/s/ Marianthe S. Mewkill


Name:		Name:

Sofia A. Rosala		Marianthe S. Mewkill

Title:		Title:

Vice President & Assistant Sec.		COO & EVP

Schedule A

to the

Sub-Advisory Agreement

between

SEI Investments Management Corporation

and

Smith Breeden Associates, Inc.

As of September 29, 2005

SEI INSTITUTIONAL MANAGED TRUST

Core Fixed Income Fund

Large Cap Diversified Alpha Fund

Schedule B